[Bug 1309818] Re: pwritev() doesn't work anymore on i386

[Michael Ferguson]

I'm also encountering this bug  with updated Ubuntu 14.04 but only on
32-bit installations.

I have another program to reproduce it, included below. This program
makes it to printing out OK on the 64-bit version.

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/uio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <assert.h>

int main() {
  struct iovec vec[1];
  char* buf;
  size_t buflen = 4096;
  char* data = "aaaaaaaaaaaaaaaaaaaa";
  int datalen = strlen(data);
  int fd;
  ssize_t got;

  
  buf = malloc(buflen);
  assert(buf);
  vec[0].iov_base = buf;
  vec[0].iov_len = buflen;

  // open file
  fd = open("tmp.data", O_RDWR | O_CREAT, S_IRWXU);
  assert(fd>=0);
  
  // copy data to buf
  memset(buf, 0, buflen);
  memcpy(buf, data, datalen);
  vec[0].iov_base = buf;
  vec[0].iov_len = datalen;
  // write data
  got = pwritev(fd, vec, 1, 0);
  //got = pwrite(fd, buf, datalen, 0);
  if( got == - 1 ) perror("in write");
  assert(got == datalen);
 
  // clear buf
  memset(buf, 0, buflen);
  // read data
  vec[0].iov_base = buf;
  vec[0].iov_len = buflen;
  got = preadv(fd, vec, 1, 0);
  //got = pread(fd, buf, buflen, 0);
  if( got == - 1 ) perror("in read");
  assert(got == datalen);
  // check data
  assert(0 == memcmp(data, buf, datalen));
 
  close(fd);
  unlink("tmp.data");

  printf("OK\n");

  return 0;
}

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https://bugs.launchpad.net/bugs/1309818

Title:
  pwritev() doesn't work anymore on i386

Status in eglibc package in Ubuntu:
  New

Bug description:
  I just upgraded to Trusty, and the following programs fails on x86:

  #include <stdio.h>
  #include <stdint.h>
  #include <sys/uio.h>
  #include <string.h>
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <fcntl.h>

  int main()
  {
  	char *str0 = "hello ";
  	char *str1 = "world\n";
  	struct iovec iov[2];
  	ssize_t nwritten;
  	int fd = open("test.txt", O_CREAT | O_WRONLY);

  	iov[0].iov_base = str0;
  	iov[0].iov_len = strlen(str0);
  	iov[1].iov_base = str1;
  	iov[1].iov_len = strlen(str1);

  	nwritten = pwritev(fd, iov, 2, 0);
  	if(nwritten < 0)
  		perror("pwritev");

  	return 0;
  }

  Compiled without any flags, I see:

  $ ./test
  pwritev: File too large

  And, from strace, I can see the offset parameter is handled wrongly by
  (presumably) libc:

  ...
  pwritev(3, [{"hello ", 6}, {"world\n", 6}], 2, 577730142772658176) = -1 EFBIG (File too large)
  ...

  If I compile with -D_FILE_OFFSET_BITS=64, everything is right, but is
  not a solution for my problem as I can't use that flag in my program.

  I reported this here because it doesn't seem to happen on Debian sid,
  but let me know if I have to report it upstream.

  $ lsb_release -rd
  Description:	Ubuntu 14.04 LTS
  Release:	14.04

  $ apt-cache policy libc6
  libc6:
    Installed: 2.19-0ubuntu6
    Candidate: 2.19-0ubuntu6

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